1. Field of the Invention
The present invention relates to a voltage adjusting circuit, and more particularly, to a discharging circuit which can avoid affecting an input voltage source when a level pull-up circuit performs a discharging operation, wherein the discharging circuit only requires a simple circuit scheme to be applied to the level pull-up circuit.
2. Description of the Prior Art
In general, there are mainly two kinds of discharging schemes of the conventional discharging circuit. Please refer to FIG. 1. FIG. 1 shows a simplified diagram of a first kind of conventional discharging circuit 10 in accordance with the prior art. As shown in FIG. 1, the discharging scheme of the conventional discharging circuit 10 performs the discharging operation on an output voltage Vout of the discharging circuit 10 directly toward an input voltage source Vin of the discharging circuit 10 by turning on (i.e. conducting) a switch element 12. Although the discharging circuit 10 does not need a complex circuit design, when the voltage difference between the output voltage Vout and the input voltage source Vin exceeds a specific value, the discharging circuit 10 may seriously affect the input voltage source Vin while performing the discharging operation.
Please refer to FIG. 2. FIG. 2 shows a simplified diagram of a second kind of conventional discharging circuit 100 in accordance with the prior art. As shown in FIG. 2, the conventional discharging circuit 100 includes a first switch element 110, a second switch element 120, and a digital counter 130. The discharging scheme of the conventional discharging circuit 100 performs the discharging operation on an output voltage Vout of the discharging circuit 100 toward a reference voltage source Vr (such as the ground voltage level 0) of the discharging circuit 10 at first by using the digital counter 130 for turning on (i.e. conducting) the first switch element 110. After a specific period, the digital counter 130 will turn off (i.e. not conduct) the first switch element 110, and turn on the second switch element 120 to perform the discharging operation on the output voltage Vout of the discharging circuit 100 toward an input voltage source Vin of the discharging circuit 100 then. Although the discharging circuit 100 does not seriously affect the input voltage source Vin while performing the discharging operation like the discharging circuit 10 shown in FIG. 1, since the specific period which the digital counter 130 switches states of the first switch element 110 and the second switch element 120 according to is determined by experience rules, the accuracy will be affected by many factors frequently and thus the accuracy is not good enough. In addition, a logic circuit is required when designing the conventional discharging circuit 100, and thus the discharging circuit 100 needs a larger circuit layout area. Therefore, cost of the conventional discharging circuit 100 is also higher.